The present invention relates generally to radio receivers and transmitters. More particularly, the present invention relates to an improved architecture for a dual band transceiver.
Dual band transceivers provide two-way radio communication on two independent frequency bands. A transceiver combines transmission circuitry and reception circuitry. Both the transmission circuitry and the reception circuitry are supplied with oscillator signals produced by a synthesizer for demodulation, modulation and other purposes.
One example of a dual band transceiver is a dual mode cellular/PCS radiotelephone. The radiotelephone operates at cellular frequencies in the 800 MHz band and at personal communication system (PCS) frequencies in the 1900 MHz band. The radiotelephone includes a dual band transceiver and associated circuitry to operate on the two bands.
In such a system, several oscillator signals are required. The receiver circuitry requires main and second local oscillator (LO) signals for both bands. The transmitter circuitry requires carrier and offset oscillator signals for both bands.
The synthesizer circuitry necessary to generate these oscillating signals has required substantial operating currents and components to implement. In portable radio equipment, such as a radiotelephone, key design goals are reduction in operating current and reduction in physical size and weight of the radio. The operating current and components needed to implement a conventional dual band transceiver are inconsistent with these design goals.
Accordingly, there is a need for a transmitter and synthesizer, which reduces parts count, physical size and operating current.